Tandem or multiple row blades are discussed in papers by Bammert, K and Staude, R., "New Features in the Design of Axial-Flow Compressors with Tandem Blades", ASME Paper No. 81-GT-113, and Wu Guochuan, Zhuang Biaonan and Guo Bingheng, "Experimental Investigation of Tandem Blade Cascades with Double Circular Arc Profiles", ASME Paper No. 85-IGT-94. These papers recite the history as well as the recent research on this subject. Heretofore, turbomachines of the pressure generating type were constructed to generate a substantial pressure within the rotating impeller blades, e.g., all centrifugal blowers and most axial flow machines. Prior art turbomachines developed at least approximately 50% of the pressure generated in the "rotor" or impeller blades and the remaining amount of pressure in the guide vanes. Prior art turbomachines did not use impeller- blades to deflect the fluid flow essentially without generating pressure therein while simultaneously generating all or substantially all of the pressure in the guide vanes. Conventional axial flow blowers generate substantial pressure within the rotating impeller blades; the degree of reaction in the rotating impeller blades is high with values up to 85%. The high pressure generated in the rotating blades produces flow leakage losses between the tips of the blades and the adjacent housing because the rotating blades must have a gap with a stationary structure in order to rotate. This leakage imposed performance and efficiency limitations on the apparatus.
Slotted turbomachine blades are known per se. My U.S. Pat. Nos. 3,075,734 and 3,195,807 relate to turboengine blades in which each blade contains a single slot of defined dimensions with a limited amount of fluid flowing through the slot. Thus, these two patents disclose two separate parts of a single blade, located in close relationship to each other, with the objective being to extend the laminar flow region of the combined blade further downstream than theretofore had been possible. Moreover, the slot formed between the two (separate) blade sections was located in the aft part of the combined blades; i.e., approximately sixty percent of the chord of the combined blade downstream from the leading edge of the combined blade. Prior art devices did not use slotted blades to provide a flow path of extended length in which the fluid is supported between adjacent blades thereby increasing the amount of flow deceleration. Prior art devices did not use separate rows of blades in which the gap between rows was located in the forward part of the combined blade.
Prior axial flow fans and centrifugal fans operated within certain specific speed .eta..sub.5 ranges. Prior art axial flow fans and centrifugal fans could not be operated within reduced specific speed ranges in which the turbomachine of this invention can be operated.
Prior art impeller blades which generated substantial pressure as fluid flowed therethrough could not be used to deflect the fluid by more than approximately 49.degree. because stalling occurred where any larger amount of deflection was attempted due to the inability of the blades to discharge fluid therefrom.
Maximum pressure coefficients at the point of maximum efficiency for prior art axial flow blowers have been on the order of 0.8; pressure coefficients for prior art radial blowers have been approximately 1.1 with maximum values up to 1.4. Prior art axial flow blowers did not operate at a pressure coefficient of 1.0 and certainly not as large as 1.4 to 3.6 and more. Prior art centrifugal fans did not operate at a pressure coefficient of 3.0 or more.
Vector flow diagrams of prior art axial flow impeller blades show that the circumferential components of the relative velocities w.sub.u1 and w.sub.u2 are in the same direction and are opposed to the direction of the circumferential impeller velocity direction (u). Vector flow diagrams of prior art impeller blades did not show the flow vector of the circumferential component of relative velocity (w.sub.u2) of said impeller blades at the outlet to be in the same direction as the circumferential velocity (u).
Prior art diffusers provided a flow path of substantial length with converging and/or diverging flow directing surfaces to assist in the recovery of static pressure from dynamic pressure. Prior art diffusers conventionally are of considerable length requiring extra cost to manufacture and additional space to house the diffuser. Prior art diffusers did not include means for removing a portion of the boundary layer from the surfaces thereof and returning same to the fluid flow path at a point upstream of the place where same had been removed. Prior art diffusers did not include means to remove a portion of the boundary layer and use said removed boundary layer to cool the motor of the pump or blower before it was returned to the fluid flow path.
Previously, a complex analysis of axial flow blower blades was involved to determine the limits of flow deflection and deceleration as functions of entrance angle, solidity and blade profile configuration. Maximum flow deflection of the numerous blades has been published in NACA Technical Note 3916, "Systematic 2-Dimensional Cascade Test of NACA 65-Series Compressor Blades at Low Speeds" by L. Joseph Herrig, James C. Emery and John A. Erwin, February, 1957. It was unknown in the prior art that multiple row blades with different numbers of blades in each row and optimum blade solidity can achieve higher flow deflection angles than conventional blades.